Shrinking to fit, AMC forces the hand of photomask makers

Mark A. DeSorbo

FRANKLIN, MA—AS SEMICONDUCTOR manufacturing platforms plunge deep into the sub-micron realm, molecular contamination becomes even more of a critical threat as it can change the course of the process and completely obliterate the product.

Airborne molecular contamination (AMC) has indeed forced many industries to shift gears and address malignant microcosms, and that has led to further use of lasers, the development of optical and real-time particle counters as well as a revisit to such methods as Raman spectroscopy.

Most recently, attention has turned to advanced chemical filtration in the photomask writing process, where atmospheric acids, bases and organics present a threat of contamination.

“The technology is heading below 100-nanometer platforms,” says James Hudzik, mask market product sales manager for Micronic Laser Systems AB (Taby, Sweden), a manufacturer of laser pattern generators photomask production. “It's getting smaller and smaller. To create those smaller features, you have to have smaller features on the mask.”

Micronic recently announced that it will use Extraction Systems Inc.'s (Franklin, MA) chemical filtration technology to protect its new line of Sigma laser pattern generators from AMC that is commonly found in fab environments.

Hudzik says Extraction's filter system prevents contaminants from damaging the Sigma's optical elements, while protecting the photoresists used to print chip designs on photomasks.

“We are committed to process stability and machine productivity in mask making,” says Hans Buhre, Micronic's chief technology officer. “Extraction's experience and capabilities in molecular contamination measurement and control have helped us solve these potential problems in the design phase, and allowed us to focus on developing faster, higher-resolution mask writing products.”

The photomask sector is of rather strategic importance to the semiconductor industry, says Devon Kinkead, president and chief executive of Extraction. The main objective, he says, is to foster cost-effective photomask production, adding that deep ultraviolet light and chemically amplified photoresists will be “an enabling technology in this era of subwavelength feature sizes.”

“The mask industry faces many new technology and process challenges as we move into even more complex optical proximity correction (OPC), phase shift, membrane and reflective masks,” Kinkead says.

Technologies, like Extraction's chemical filtration, will alleviate what Hudzik says is a double-edged challenge facing the photomask industry.

The mask, the negative within for photolithography process, is now four to five times the size of currently used chip platforms, which produce even tinier patterns of circuitry. Smaller patterns mean shorter wavelengths, which are even more sensitive to AMC.

“It's a tool issue and a process issue, which can ruin wafers,” he says. “And what's not understood in deep ultraviolet photoresist is the effect of bases, acids and organics on the tool and the process. Contamination alters the process and it's blurring the pattern and rendering the chip useless.”

Hudzik adds the photomask industry needs to make a unified effort to literally shrink the mask with the times.

“As technology gets smaller and smaller, mask makers will be forced to get smaller, too,” Hudzik says. “The photomask industry has to come up that ramp.”

The Micronic mask is four to five times the size of currently used chip platforms, which produce even tinier patterns of circuitry. Photomask industry players believe the mask needs to shrink with the times.
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